Prior art time division multiplexed (TDM) telephone systems provide network services to individual calls by internally redirecting those calls within an exchange to one or more individual network service provider equipment items which may be co-located in the exchange, either within a switch, or within a rack or row of racks associated with a switch. Network service provider devices provide services to calls passing through an exchange. Such devices may include network announcers, intelligent peripheral devices, universal tone receivers (UTRs) and universal tone generators (UTGs). Network announcers may comprise simple announcement devices for sending messages such as “all international lines are busy” or the like. Such machines have historically developed from simple analogue devices for playing pre-recorded messages, more recently to digital devices for playing pre-stored messages. A universal tone generator provides dial tones to a call, and a universal tone receiver detects tone dial digits from a call.
Referring to FIG. 1 herein, there is illustrated schematically a general architectural overview of a prior art exchange comprising a conventional prior art TDM switch 100, a network announcer device 101, an intelligent peripheral device 102, and a universal tone receiver/universal tone generator (UTR/UTG) device 103. Typically, network service provider components 101-103 may be co-located with the TDM switch within an exchange building in an array of racks as illustrated schematically in FIG. 2 herein. A conventional circuit switched TDM call comprises first and second channels between an originating source device, eg a first telephone device, and a receiving destination device, eg a second telephone device. Each circuit carries traffic data, eg voice or fax/modem traffic data in a first direction on the first channel from the first device to the second device and in a second direction on the second channel from the second device to the first device. A call on an incoming (originating) TDM circuit or trunk may be received by TDM switch 100 at an input port 104 of the switch, routed through the switch via one or more network service provider devices associated with the switch and routed through an output port 105 of the switch. Network services are provided by network service modules comprising for example the network announcer, intelligent peripheral, or UTR/UTG.
In the conventional network, such network services are required at many points in the network. For example in prior art legacy networks, when a number is dialed, parts of the number are echoed from exchange to exchange across the network. Each exchange in a path has to separately recognize it's portion of the dialed number and route the call on that basis. This process incurs delays at every exchange the call passes through. In legacy networks, it is common that some types of service provider for example the UTR/UTG are provided at each exchange in the network, whilst other types of service provider eg the network announcer or intelligent peripheral may appear only at specified places in the network and not on every exchange.
In each case, in prior art legacy networks the network service provider comprises a discrete card or rack of equipment within an exchange. The exchange, when it receives a call either directly from a subscriber or from an incoming trunk recognizes dialed digits or an off-hook signal, and internally switches the call to an appropriate service provider component. This incurs delays throughout the network.
Referring to FIG. 3 herein, there is illustrated components of an exchange which detect a call and connect the call to a UTR and UTG. As a call is built up from originating source to destination, when a phone 300 goes off hook, a seize detect element 301 of a local exchange 302 detects that the phone has gone off hook. This causes an electronic connection of the call to a universal tone generator 303 which applies a dial tone back to the call.
In the prior art switches, the whole call must be switched entirely through the internal switch network. Each switch takes time to re-direct the call to the appropriate network service provider component. In practice, the physical media used to connect each rack and component is electrical or optical cabling using T1/E1 or higher rate trunks. Where higher rates are used there is an inefficiency in re-multiplexing the data to a higher rate and then de-multiplexing data within the relevant service provider function. Normally, the whole speech path of a call has to be passed to the relevant service provided component and that component then has to pass the speech path back to the switching fabric of the switch for completing a path to the outgoing trunk, thereby incurring delays at the switch in connecting a call to the network service provider devices.